Conventionally, in an apparatus of this type, an electronic part held by a chip holding tool is lowered toward a substrate, and ultrasonic bonding is started when the electronic part is brought into contact with the substrate. Accordingly, it is necessary to detect the contact position. In order to make the tact time as short as possible, a chip holding tool is first lowered at a relatively high speed from a transfer position (the initial position of the chip holding tool, indicated by symbol A in FIG. 2) by a predetermined distance (hereinafter also referred to as the initial moving distance or the initial moving amount, which is indicated by symbol 1 in FIGS. 2 and 9). Thereafter, for the purpose, for example, of enhancing the accuracy with which the contact position is detected, the tool is lowered at a relatively low speed until the contact start, detecting the contact through a contact detecting device (a load cell or the like), etc.
However, in this conventional method, due to thermal expansion of the substrate holding portion (substrate holding means) and product variation (dimensional deviation), mounting errors, etc. of the electronic part and the substrate, variation is generated in the distance between the transfer position A and the substrate, which may lead to the following problem.
That is, to achieve an improvement in terms of productivity by shortening the tact time, it is general practice to set the initial moving distance 1 (the distance through which the chip holding tool is moved at a relatively high speed) to a predetermined distance. If, however, there is such variation as mentioned above, the distance between the transfer position A and the substrate may become shorter, and, as shown in FIG. 10A, the electronic part and the substrate may collide with each other, resulting in a defective product or a deterioration in the contact position detecting accuracy since a sufficient contact detection distance Ls (see FIG. 2) cannot be ensured.
On the other hand, when the distance from the transfer position A to the substrate is rather long due to the variation as mentioned above, the contact detection distance (searching distance) through which the tool is moved at a relatively low speed for contact detection after the movement through the initial moving distance 1 becomes rather long as shown in FIG. 10B, resulting in an increase in tact time and a deterioration in productivity.
In view of this, in order to avoid inadvertent contact of the electronic part with the substrate and a deterioration in contact position detection accuracy while maintaining high productivity, it might be possible to correct the initial moving distance 1 according to the above-mentioned variation, etc.
For example, Japanese Patent Application Laid-Open No. 2000-174498 discloses a system in which the above-mentioned initial moving distance is corrected based on the contact start position as detected with the first substrate, using the corrected moving distance for the mounting on the substrates from the second one onwards.
However, in the above system, the warpage of the substrates from the second one onward is regarded as practically the same as the warpage of the first substrate, using the correction result obtained with respect to the first substrate for the substrates from the second one onward, too, with the result that a sufficient correction accuracy cannot be ensured.